This invention relates to an electronic circuit for use in a time division multiple access (often abbreviated to TDMA) system. The TDMA system is widely used in various radio communication units. One of the radio communication units may be a digital radio telephone set using .pi./4-shift QPSK modulation. For convenience of understanding, description will be mainly directed to the digital radio telephone set.
The telephone set comprises an electronic circuit which is supplied with a sequence of data signals on carrying out a predetermined communication to produce a data burst under control by a burst control pulse which is known in the art. The data burst carries the data signal sequence.
In the manner which will later be described, the conventional electronic circuit comprises a signal producing and a signal processing circuit. Each of the data signals is divided into a plurality of symbols each of which is represented by two bits. By the use of an impulse response which is known in the art, the signal producing circuit carries out an arithmetic operation on a current one of the symbols to produce a local signal under control by the burst control pulse.
The signal processing circuit is for processing the local signal into the data burst during presence of the burst control pulse. The data burst has a plurality of leading edges. It is assumed that the leading edges may be different from one another in form. This is because the impulse response is produced dependent on several symbols previous to the current symbol.
The telephone set has a communication zone in which the predetermined communication can be carried out. It is to be noted that the communication zone has an extent which is determined dependent on each of the forms of the leading edges. Inasmuch as the leading edges may have various forms, it is difficult in the electronic circuit to control the extent of the communication zone.